Base station and radio terminal

ABSTRACT

A base station for a wireless LAN system has physical layers corresponding to channels, and a MAC layer. The physical layers each transmits and receives a radio signal conforming to an IEEE 802.11 standard using a corresponding channel. When transmitting, the MAC layer divides an entire data frame conforming to the standard from a head of the data frame, in accordance with a transmission rate of each physical layer, and allots the divided data frame to the physical layers so that burst times of the channels are substantially equal. When receiving, the MAC layer combines data frames received via channels through operations opposite to those performed when transmitting.

TECHNICAL FIELD

The present invention relates to a base station and a radio terminal fortransmitting and receiving a radio signal according to the IEEE 802.11Wireless LAN Standards. More specifically, the present invention relatesto a base station and a radio terminal for widening a band using aplurality of communication channels.

BACKGROUND ART

A conventional radio communication system (wireless LAN communicationsystem) will be explained. At present, products according to the IEEE802.11b standard, the IEEE 802.11a standard, and the like, which arestandardized according to the American IEEE 802.11 Wireless LANStandards (see Non-Patent Literature 1: IEEE 802.11 fromhttp//standards.ieee.org/getieee802/802.11.html) have been marketed asapparatuses for constructing home/office high-speed wireless networksystems.

A wireless LAN according to the IEEE 802.11b standard (see Non-PatentLiterature 2: IEEE 802.11b) has a maximum physical transmission rate of11 megabits per second, using a 2.4-gigahertz band and complementarycode keying (CCK) as a modulation scheme. A wireless LAN according tothe IEEE 802.11a standard (see Non-Patent Literature 3: IEEE 802.11a)has a maximum physical transmission rate of 54 megabits per second,using a 5-gigahertz band and orthogonal frequency division multiplex(OFDM) as a modulation scheme. A wireless LAN according to the IEEE802.11g standard, for which specifications of the standard are beingconsidered, has a maximum physical transmission rate of 54 megabits persecond, using a 2.4-gigahertz band and the ODFM as a modulation scheme.

The conventional radio communication systems have, however, a problem inthat an effective rate indicating at what rate a data stream can beactually transmitted is often equal to or lower than half the maximumphysical transmission rate.

Specifically, a data stream to be transmitted, for example, is dividedinto a plurality of data packets. Each data packet is added with headerinformation including information for transmission control includingdestination/sender IP addresses, a packet length, a packet number, andthe like and with information for error correction control. The datapackets added with the information are received by a lower layer asinternational protocol (IP) packets. In a media access control (MAC)layer, a data frame is also added with header information includinginformation for transmission control including destination/sender MACaddresses, a frame length, and the like, as well as information forerror correction control and the data frame may be encoded and addedwith decoding information to be received by a physical layer. In thephysical layer, the data frame is added with header informationincluding information for transmission control including a modulationscheme, a frame length, and the like, as well as a preamble forsynchronization and the like to be transmitted.

Furthermore, the base station or each radio terminal performs carriersensing for the radio channel before transmission of the radio frame. Ifthe base station or radio terminal confirms that the channel is beingused (the channel is busy), it refrains from transmitting the radioframe. After confirming that the channel is not being used (the channelis idle), the base station or radio terminal uses a random access schemecalled carrier sense multiple access/collision avoidance (CSMA/CA) fortransmitting the radio frame. A base station or a radio terminaldesignated by the MAC address returns an ACK/NACK frame indicatingwhether the radio data frame has been correctly received. If the radiodata frame has not been correctly received, the frame is retransmitted.

Accordingly, the effective rate is not equal to the physicaltransmission rate for the wireless LAN according to the IEEE 802.11b,IEEE 802.11a, or IEEE 802.11g standard. Actually, therefore, theeffective rate is equal to or less than approximately half the physicaltransmission rate, depending on the environmental conditions of thetransmission system.

Namely, if the conventional home/office wireless network system(wireless LAN) according to the IEEE 802.11a standard, the IEEE 802.11bstandard, the IEEE 802.11g standard, or the like is to performbidirectional communications for a data stream of a video signal for ahigh resolution television HDTV (High Definition Television) thatrequires, for example, approximately 20 megabits per second, theeffective rate is insufficiently low.

To solve the problem of the insufficient effective rate, there isproposed, for example, the following method disclosed in Japanese PatentApplication Laid-Open No. 2002-135304. In this method, if a broadbanddata stream, for example, is to be transmitted and received, IP packetsare allocated to a plurality of radio units operating with differentchannels to be transmitted and received under independent controls ofthe respective radio units. However, if the respective units usedifferent modulation schemes or the allocated IP packets have differentsizes, a delay is caused by processes such as rearrangement of packets,because the allocation to the radio units is carried out in IP packetunits. Furthermore, the leakage power from an adjacent channel becomeshigher than a carrier sense threshold because of the independentcontrols of the respective radio units. As a result, normal transmissioncannot be carried out.

There is also proposed the following different method. In this differentmethod, one radio unit serves as a master, and if a broad transmissionband is necessary for video transmission or the like, a sub radio unitcorresponding to a channel allocated in advance is operated as a slave.The master transmits and receives a control signal for a plurality ofradio units to acquire a radio channel access right, whereby the radiounits transmit and receive IP packets. This method has, however, thefollowing problem similarly to the above method. When the radio unitsuse different modulation schemes or the allocated IP packets havedifferent sizes, because the allocation to the radio units is carriedout in IP packet units, on one hand, reception cannot be performed evenif a radio unit has completed transmission, if another radio unit hasnot completed transmission. On the other hand, a terminal receiving IPpackets cannot perform transmission even if a radio unit has completedreception, if another radio unit has not completed reception. As aresult, the radio band cannot be efficiently used.

The present invention has been achieved in view of the above problems.It is an object of the present invention to provide a radiocommunication system (a base station and a radio terminal) capable ofimproving the throughput by efficiently using the radio band.

DISCLOSURE OF INVENTION

A base station (or a radio terminal) according to the present invention,being an apparatus for a wireless LAN system realizing band-wideningusing a plurality of communication channels, includes: a plurality ofphysical layers corresponding to the plurality of communicationchannels, and each that transmits and receives a radio signal conformingto an IEEE 802.11 standard using a corresponding communication channel;and a media access control (MAC) layer. The MAC layer, whentransmitting, divides an entire data frame conforming to the IEEE 802.11standard from a head of the data frame, in accordance with atransmission rate of each physical layer, and allots the divided dataframe to the physical layers so that burst times of the communicationschannels are substantially equal, and when receiving, combines dataframes received via a plurality of communication channels throughoperations opposite to those performed when transmitting.

According to the present invention, for example, a radio signalaccording to the IEEE 802.11a standard, the IEEE 802.11b standard, theIEEE 802.11g standard, or the like is allotted to a plurality ofcommunication channels to be transmitted to a home/office wirelessnetwork. A MAC layer sets the entire frame as a division target, andallots the frame divisions to the respective physical layers.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of a configuration of a radio communicationsystem according to the present invention;

FIG. 2 is an illustration of a configuration of a broadband radio unit;

FIG. 3 is an illustration of a data frame format according to the IEEE802.11a standard;

FIG. 4 is an illustration of a frame format when a plurality of channelsare used;

FIG. 5 is an illustration of a method for dividing/distributing MPDU;

FIG. 6 is an illustration of a data frame format according to the IEEE802.11a standard;

FIG. 7 is an illustration of a frame format when a plurality of channelsare used;

FIG. 8 is an illustration of a method for dividing a part of a frame;

FIG. 9 is an illustration of a data frame format according to the IEEE802.11a standard;

FIG. 10 is an illustration of a method for dividing a part of a frame;

FIG. 11 is an illustration of an example of dividing a frame to aplurality of channels;

FIG. 12 is an illustration of an example of a third embodiment in whicha frame is divided to a plurality of channels;

FIG. 13 is an illustration of a service field in a frame according to anIEEE 802.11 standard; and

FIG. 14 is an illustration of a communication status between radiostations that carry out communications using a plurality of channels.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Exemplary embodiments of a radio communication system (base station andradio terminal) according to the present invention will be explainedbelow in detail with reference to the accompanying drawings. Theinvention is not limited by the embodiments.

First Embodiment

FIG. 1 is an illustration of a configuration of a radio communicationsystem (radio network for home/office) according to the presentinvention. This radio communication system includes a base station (AP)1 and a plurality of radio terminals (STA) 2A, 2B, . . . . The basestation 1 has a gateway for mutual connection to an access line (forexample, Ethernet®, xDSL, CATV, FTTH, or the like) connecting to anaccess network that constitutes a wired or wireless externalcommunication network,

The base station 1 includes a communication unit system 11 thatterminates a wired or wireless access line connecting to an accessnetwork, and that transmits reception information from the accessnetwork to specific radio terminals 2A, 2B, . . . , through a wirelessnetwork in a home/office. This communication unit system 11 includes anaccess terminal unit 13 that terminates the access line, a signalinterface unit 14 (corresponding to, for example, a router or a bridge)that controls a mutual conversion signal formats between a signal of theaccess network and signals of the radio terminals 2A, 2B, . . . , abroadband radio unit 15 that transmits and receives a radio signalaccording to the IEEE 802.11a standard, the IEEE 802.11b standard, theIEEE 802.11g standard, or the like to and from the wireless network inthe home/office through a plurality of channels, and antennas 12-1,12-2, . . . . While a plurality of antennas are connected to thebroadband radio unit 15 in this embodiment, the number of antennas maybe one.

The radio terminals 2A and 2B include information equipment main bodies21A and 21B such as personal computers, PDAs, or television receivers,and terminal unit systems 22A and 22B controlling transmission andreception of data between the information equipment main bodies 21A and21B and the communication unit system 11 of the base station 1,respectively. The terminal unit systems 22A and 22B include terminalinterface units 24A and 24B controlling mutual conversion of signalformats between a signal from the base station 1 or the other radioterminal and a signal from the information equipment main bodies 21A and21B, broadband radio units 25A and 25B that transmit and receive a radiosignal according to the IEEE 802.11a standard, the IEEE 802.11bstandard, the IEEE 802.11g standard, or the like to and from thehome/office wireless network through a plurality of channels, andantennas 23A-1, 23A-2, . . . , and 23B-1, 23B-2, . . . , respectively.Although a plurality of antennas are connected to the respectivebroadband radio units 25A and 25B in this embodiment, the number ofantennas connected to each broadband radio unit may be one. Furthermore,while the radio communication system in which the radio terminals areconnected to the base station is described in this embodiment, thepresent invention is not limited to this embodiment. The presentinvention is also applicable to, for example, an ad hoc network in whichradio terminals construct their independent network and carry outcommunications.

FIG. 2 is an illustration of a configuration of the broadband radiounits 15 and 25 according to this embodiment. Each of the broadbandradio units 15, 25A, and 25B (the units 25A and 25B correspond to theunit 25 shown in FIG. 2) includes a host interface unit (Host Interface)33 for connecting the broadband radio unit 15, 25A or 25B to the signalinterface unit 14 or the terminal interface unit 24A or 24B, a mediaaccess control (MAC) layer 32 according to the IEEE 802.11 standard (a,b, e, f, g, h, i, or the like) and expanded to satisfy this embodiment,and a plurality of physical layers (PHYs) 31 (corresponding to PHYs31-1, 31-2, 31-3, . . . ) operating with a plurality of differentchannels conforming to the IEEE 802.11a standard, the IEEE 802.11bstandard, IEEE 802.11g standard, or the like.

The MAC 32 corresponds to an expansion of the IEEE 802.11 standard (a,b, e, f, g, h, i, or the like). If the physical layers corresponding tothe plurality of channels are not used, the MAC 32 operates according tothe IEEE 802.11 standard. A TxControl unit 37 in the MAC 32, performsframe allotment for transmitting a transmission frame through aplurality of channels, frame check sequence (FCS) addition, time stampaddition, control of readout from a buffer, backoff processing, andautomatic generation of at least one of an request to send (RTS) frame,a clear to send (CTS) frame, and an ACK frame. An RxControl unit 36performs combining of frames received through the plurality of channels,FCS check, write process to a buffer, address decoding, and channelstatus processing.

The MAC 32 also includes a plurality of Transmission (Tx) units 34(corresponding to Tx units 34-1, 34-2, 34-3, . . . ) and Reception (Rx)units 35 (corresponding to Rx units 35-1, 35-2, 35-3, . . . ). Each ofthe Tx units 34 and Rx units 35 performs issuance of a primitive to thecorresponding physical layer, data write process, and data readoutprocess.

Accordingly, the MAC 32 is configured so that the Tx units 34 and the Rxunits 35 each performs the necessary processes on the individual frame,and the TxControl unit 37 and the RxControl unit 36 perform thenecessary processes on all the frames.

A Protocol control unit 38 functions not only to control acquisition ofan access right with respect to each channel based on a CSMA/CA protocolbut also to determine a transmission rate of each channel, a frameallotment ratio between the channels, a transmission data amount in eachchannel, and the like.

The MAC 32 further includes a transmission and reception buffer, anencoding unit, an authentication management unit, and the like althoughnot shown in FIG. 2. Each physical layer 31 includes an RF unit having aBaseBand unit that modulates a signal from the MAC 32 to a transmissionsignal and demodulates a reception signal to a signal to be transmittedto the MAC 32, an up-converter/down-converter converting the signaltransmitted from/to to the BaseBand unit to a desired signal, a poweramplifier, and the like.

Operations of the radio communication system will next be explained.FIG. 3 is an illustration of a data frame format according to the IEEE802.11a standard and FIG. 4 is an illustration of a frame format when aplurality of channels (three channels) are used. FIGS. 3 and 4 indicatethat if a frame is allotted to a plurality of channels to betransmitted, the burst times of the channels are equal. It is noted thatdata bits per OFDM symbol (N_(DBPS)) is specified in the IEEE 802.11astandard and indicates a number of data bits that can be transmitted perOFDM symbol. In this embodiment, for convenience of explanation only, anumber of octets that can be transmitted per OFDM symbol is defined asdata octets per OFDM symbol (N_(DOPS)). That is, N_(DOPS) equalsN_(DBPS)/8.

A data frame (MPDU) 40 according to the IEEE 802.11a standard shown inFIG. 3 includes an MAC header 41, an LLC header/SNAP header 42, a framebody 43, and an FCS 44. If the MPDU 40 is transmitted from the MAC 32 tothe physical layers 31, an OFDM signal 50 is transmitted in the order ofa preamble 51 for synchronization, a SIGNAL 52 including at least one ofa transmission rate, a transmission data length, and the like, and DATA53 including a SERVICE field and a transmitted part of the MPDU 40. Aguard interval included between the OFDM symbols and changes in a bitarrangement order and in the number of bits due to modulation in thephysical layers 31 are not shown.

FIG. 4 is an illustration of frame division statuses of the MPDU 40among the plurality of channels, MPDUs 40-1, 40-2, and 40-3 in therespective channels after the division, and OFDM signals 50-1, 50-2, and50-3 in the respective physical layers 31-1, 31-2, and 31-3.

In this embodiment, all of the MAC header 41, the LLC header/SNAP header42, the Frame Body 43, and the FCS 44 specified by an IEEE 802.11standard are a target of the division. As shown in FIG. 5, the MPDU 40is divided from a head of the MPDU 40 in units of N_(DOPS) according totransmission rates of the respective physical layers 31-1, 31-2, and31-3 (divisions corresponding to an MAC header 41-1, an LLC header/SNAPheader 42-2, frame bodies 43-1, 43-2, and 43-3, and an FCS 44-2 shown inFIG. 4) into divisions. Each physical layer receives a unit of data,which can be transmitted with one OFDM symbol. FIG. 5 is an illustrationof a method for dividing/allotting the MPDU 40. In FIG. 4, therefore,the OFDM signals 50-1, 50-2, and 50-3 on the respective physical layershave burst times that are substantially equal.

Although not shown in the drawings, since the ACK frame includes onlythe MAC header and the FCS, the ACK frame is transmitted through eachchannel without being divided. If a reception side receives one ACKframe normally, that frame is recognized as the ACK frame. Therefore,retransmission of data due to a failure to receive the ACK frame occursless frequently, thereby improving the system throughput. Likewise, acontrol frame such as an RTS/CTS having a short frame length, a dataframe having a short frame length, a management frame, or the like, istransmitted at a same rate through the channels without being divided.If the reception side receives one of the frames transmitted through thechannels, that frame is recognized as the transmitted frame. Therefore,retransmission of data occurs less frequently, thereby improving thesystem throughput. To a system according to the IEEE 802.11a standard,the IEEE 802.11b standard, the IEEE 802.11g standard, or the like, aband reservation time and the like are notified at the same time.

The division and allotment according to this embodiment will now beexplained. The protocol control unit 38 determines transmission rates ofthe channels through which the respective physical layers 31-1, 31-2,and 31-3 carried out communications, and notifies at least one oftransmission frame lengths, the transmission rates of the respectivechannels, a number of channels used, and the like to the TxControl unit37.

The TxControl unit 37 is required to designate the transmission rate,the data length, and the like for each channel using a TXVECTOR beforetransmission. The TxControl unit 37 thus performs the following divisionand allotment to the respective channels in response to the notificationfrom the protocol control unit 38.

A method for calculating a number of octets of a DATA portion and a datalength in each channel, which are required for the division andallotment will be explained. For convenience of explanation, the exampleof three channels (the physical layer 31-1: Channel-A, the physicallayer 31-2: Channel-B; and the physical layer 31-3: Channel-C) will beexplained.

A number of OFDM symbols N required for transmission of the MPDU isrepresented by the following Equation (1), where, for example, a size ofthe MPDU including the MAC header, the LLC header, the SNAP header, theframe body, and the FCS is L [octets], the transmission rates of therespective channels are RATE (a), RATE (b), and RATE (c) [megabits persecond], the numbers of octets per OFDM symbol in the respectivechannels are N_(DOPS) (a), N_(DOPS) (b), and N_(DOPS) (c) [octets], andthe number of channels is k.

$\begin{matrix}{N = {{{floor}\left\lbrack \frac{\begin{matrix}{\left( {{{Frame}\mspace{14mu}{length}} + k} \right) -} \\\left( {{Number}\mspace{14mu}{of}\mspace{14mu}{octets}\mspace{14mu}{transmittable}} \right. \\\left. {{with}\mspace{14mu}{head}\mspace{14mu}{OFDM}\mspace{14mu}{symbol}} \right)\end{matrix}}{\begin{matrix}\left( {{Number}\mspace{14mu}{of}\mspace{14mu}{octets}\mspace{14mu}{transmittable}} \right. \\\left. {{with}\mspace{14mu}{OFDM}\mspace{14mu}{symbol}} \right)\end{matrix}} \right\rbrack} + 1}} & (1)\end{matrix}$

In the Equation (1), floor [·] denotes a rounding up of decimal values,and “Frame length+k” takes into consideration of a Tail bit. Further,RATE (a)≧RATE (b)≧RATE (c), and the number of OFDM symbols does notinclude a number of symbols of a SIGNAL field transmitted by BPSK(Binary Phase Shift Keying: R=1/2). Furthermore, a head OFDM symbol hastwo octets less than other symbols because of the SERVICE field, whichis two octets.

A general equation of the number of OFDM symbols N can be represented bythe following Equation (2).

$\begin{matrix}\begin{matrix}{N = {{{floor}\left\lbrack \frac{L\; + \; k\; - \;\left( \;{{\sum\limits_{x\; = \; 1}^{\; k}\;{N_{\;{DOPS}}(x)}}\; - \;{2\; k}} \right)}{\;{\sum\limits_{x\; = \; 1}^{\; k}\;{N_{\;{DOPS}}(x)}}} \right\rbrack} + 1}} \\{= {{floor}\left\lbrack \frac{L + {3k}}{\sum\limits_{x = 1}^{k}{N_{\;{DOPS}}(x)}} \right\rbrack}}\end{matrix} & (2)\end{matrix}$

The number of OFDM symbols when there are three channels (CHs) can be,therefore, represented by the following Equation (3).

$\begin{matrix}\begin{matrix}{N = {{{floor}\left\lbrack \frac{\begin{matrix}{\left( {L + 3} \right) - \left( {{N_{DOPS}(a)} + {N_{DOPS}(b)} +} \right.} \\\left. {{N_{DOPS}(c)} - 6} \right)\end{matrix}}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} + 1}} \\{= {{floor}\left\lbrack \frac{L + 9}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack}}\end{matrix} & (3)\end{matrix}$

Equations for calculating the frame lengths in the respective channelscan be derived from the Equation (3) into the following Equations (4) to(6) where the frame lengths in the channels are LENGTH (A), LENGTH (B),and LENGTH (C), respectively. The frame is allotted in descending orderof transmission rate (starting from the Channel-A). The Equations (4)represent a case where a final data of the MPDU ends in the Channel-A,the Equations (5) represent a case where the final data of the MPDU endsin the Channel-B, and the Equations (6) represent a case where the finaldata of the MPDU ends in the Channel-C.

$\begin{matrix}{\begin{matrix}{{{LENGTH}(A)} = {{\left( {N - 1} \right) \times {N_{DOPS}(a)}} - 3 +}} \\{{mod}\left\lbrack \frac{L + 9}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack}\end{matrix}{{{LENGTH}(B)} = {{\left( {N - 1} \right) \times {N_{DOPS}(b)}} - 3}}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - 3}}\left( {{Where},{{{mod}\left\lbrack \frac{L + 9}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} \leq {N_{DOPS}(a)}}} \right)} & (4) \\{{{{{{LENGTH}(A)} = {{N \times {N_{DOPS}(a)}} - 3}}{{LENGTH}(B)}} = {{\left( {N - 1} \right) \times {N_{DOPS}(b)}} - 3 + \left( {{{mod}\left\lbrack \frac{L + 9}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} - {N_{DOPS}(a)}} \right)}}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - {3\left( {{Where},{{N_{DOPS}(a)} < {{mod}\left\lbrack \frac{L + 9}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} \leq {{N_{DOPS}(a)} + {N_{DOPS}(b)}}}} \right)}}}} & (5) \\{{{{LENGTH}(A)} = {{N \times {N_{DOPS}(a)}} - 3}}{{{LENGTH}(B)} = {{N \times {N_{DOPS}(b)}} - 3}}\begin{matrix}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - 3 +}} \\{{\text{(}{{mod}\left\lbrack \frac{L\; + \; 9}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack}} -} \\\left. {{N_{DOPS}(a)} - {N_{DOPS}(b)}} \right)\end{matrix}\left( {{Where},{{{N_{DOPS}(a)} + {N_{DOPS}(b)}} < {{{mod}\left\lbrack \frac{L\; + \; 9}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack}\mspace{14mu}{or}}},{{{mod}\left\lbrack \frac{L\; + \; 9}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack} = 0}} \right)} & (6)\end{matrix}$

Namely, the protocol control unit 38 calculates the frame lengthstransmitted through the respective channels, and the TxControl unit 37integrally performs the FCS addition, the time stamp addition, thecontrol of readout from the buffer, the back-off processing, and thelike according to the frame division and the allotment.

Each of the Tx units 34-1, 34-2, and 34-3 performs the issuance of theprimitive, the data writing process, and the like to the correspondingphysical layer to exchange data and the control signal with the physicallayer. Each of the physical layers 31-1, 31-2, and 31-3 generates atransmission data frame from the data transmitted from the correspondingTx unit and transmits the generated transmission data frame.

For reception, the Rx units 35-1, 35-2, and 35-3 perform reception ofthe primitives, reading, and the like from the respective physicallayers 31-1, 31-2, and 31-3. The RxControl unit 36 receives results ofthe reception and the reading. The RxControl unit 36 integrally performsthe combining of the frames received through the channels, the FCScheck, the writing to the buffer, the address decoding, the channelstatus processing, and the like. If it is required to transmit the ACKframe, the RxControl unit 36 transmits the ACK frame through theprotocol control unit 38 if necessary.

In this embodiment, if the final data of the MPDU ends in the Channel-A,the numbers of OFDM symbols in the Channel-B and the Channel-C are lessthan that of the Channel-A by one. If the final data of the MPDU ends inthe Channel-B, the number of OFDM symbols in the Channel-C is smallerthan those of the Channel-A and the Channel-B by one. In these cases,for transfer from the MAC 32 to the physical layers 31, the MAC 32detects the channel in which the number of OFDM symbols is one less thanthose in the other channels and adds Pad bits to the detected channel tomake the OFDM symbol lengths equal among all the channels. Althoughthree channels are used in this embodiment, an arbitrary number ofchannels can be used. If only one channel is used, then the division andcombining are unnecessary and the operations are similar to thoseaccording to the existing IEEE 802.11a, IEEE 802.11b, and IEEE 803.11gstandard. Further, channels which are not adjacent to each other may beused. The division and allotment according to this embodiment is only anexample, any equations may be used as long as the transmission timingand the burst times become equal among the channels.

As described above, according to this embodiment, the radio signalconforming to the IEEE 802.11a standard, the IEEE 802.11b standard, theIEEE 802.11g standard, or the like is allotted to the plurality ofcommunication channels to be transmitted to the home/office wirelessnetwork. Here, the MAC divides the entire frame as the division target,and allots the frame divisions to the physical layers. It is therebypossible to efficiently utilize the radio band, and thus greatly improvethe throughput, as compared with the conventional techniques.Furthermore, since the existing physical layers according to the IEEE802.11a, IEEE 802.11b, and IEEE 802.11g standards can be used, backwardcompatibility with respect to the existing systems can be maintained.The operations according to this embodiment are also applicable to MIMOsystems spatially having a plurality of channels.

Second Embodiment

In the first embodiment, the method for dividing the entire frame hasbeen explained. In a second embodiment, a method for dividing a part ofthe frame will be explained. Configurations of a radio communicationsystem, a base station, and a radio terminal according to thisembodiment are the same as those shown in FIGS. 1 and 2 according to thefirst embodiment. Therefore, the same reference numerals are designatedto omit descriptions thereof.

Operations of the radio communication system according to the secondembodiment will be explained. Only processes different from thoseaccording to the first embodiment will be explained.

FIG. 6 is an illustration of a data frame format according to the IEEE802.11a standard. FIG. 7 is an illustration of a frame format when aplurality of channels (three channels) are used. It is shown that when adata frame is allotted to the plurality of channels to be transmitted,burst times are equal among the channels.

In this embodiment, the data frame MPDU 40 to be transmitted includes aMAC header 41, an LLC header/SNAP header 42, a frame body 43, and an FCS44, which are specified by an IEEE 802.11 standard. The LLC header/SNAPheader 42, the frame body 43, and the FCS 44 are a target of divisionare divided from the head in units of N_(DOPS) according to transmissionrates of respective physical layers 31-1, 31-2, and 31-3 into divisions(corresponding to an LLC header/SNAP header 42-1, frame bodies 43-1,43-2, and 43-3, and an FCS 44-2 shown in FIG. 7). The divisions are fedto the physical layers in units of data that can be transmitted per OFDMsymbol. In FIG. 7, therefore, OFDM signals 50-1, 50-2, and 50-3 in therespective physical layers have burst times which are substantiallyequal.

Division and allotment according to this embodiment will now beexplained. A method for calculating a number of octets of a DATA portionand data length in each channel, which differs from the method accordingto the first embodiment, will be explained. Similarly to the firstembodiment, an example in which three channels (a physical layer 31-1:Channel-A, a physical layer 31-2: Channel-B; and a physical layer 31-3:Channel-C) are used will be explained.

A number of OFDM symbols N required for transmission of the MPDU iscalculated as illustrated in FIG. 8, where, for example, a size of theMPDU including the LLC header, the SNAP header, the frame body, and theFCS is L [octets], the transmission rates in the respective channels areRATE (a), RATE (b), and RATE (c) [megabits per second], numbers ofoctets transmitted per OFDM in the respective channels are N_(DOPS) (a),N_(DOPS) (b), and N_(DOPS) (c) [octets], and the number of channels isk.

Here, RATE (a)≧RATE (b)≧RATE (c), and the number of OFDM symbols do notinclude a number of symbols for a SIGNAL field transmitted by BPSK(R=1/2). Furthermore, a head OFDM symbol is two octets less than thoseof the other symbols because of a SERVICE field of two octets.

The number of OFDM symbols required until transmission of the MAC headerat the lowest RATE (c) is completed is calculated by the followingEquation (7).

$\begin{matrix}{{N_{{MAC}\_{HEADER}}(c)} = {{floor}\left\lbrack \frac{\begin{matrix}{{SERVICE\_ FIELD} +} \\{MAC\_ HEADER}\end{matrix}}{N_{\;{DOPS}}(c)} \right\rbrack}} & (7)\end{matrix}$

An amount of data transmitted in the other channels during that periodis then calculated.

$\begin{matrix}{L_{HEADER} = {\sum\limits_{x = 1}^{k}\left( {{{N_{\;{DOPS}}(x)} \times {N_{{MAC}\_{HEADER}}(c)}} - {SERVICE\_ FIELD} + {MAC\_ HEADER}} \right)}} & (8)\end{matrix}$

Accordingly, an amount of the remaining data equals L-L_(HEADER). Thenumber of OFDM symbols required to transmit the remaining data is,therefore, represented by the following Equation (9). A general equationfor the number of OFDM symbols N required to transmit data is thefollowing Equation (10).

$\begin{matrix}{N_{DATA} = {{floor}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + k}{\sum\limits_{x = 1}^{k}{N_{\;{DOPS}}(x)}} \right\rbrack}} & (9)\end{matrix}$

$\begin{matrix}\begin{matrix}{N = {{N_{{MAC}\_{HEADER}}(k)} + N_{\;{DATA}}}} \\{= {{{floor}\left\lbrack \frac{{SERVICE\_ FIELD} + {MAC\_ HEADER}}{N_{\;{DOPS}}(c)} \right\rbrack} +}} \\{{floor}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + k}{\sum\limits_{x = 1}^{k}{N_{\;{DOPS}}(x)}} \right\rbrack}\end{matrix} & (10)\end{matrix}$

The number of OFDM symbols N when three channels are used can thereforebe represented by the following Equation (11).

$\begin{matrix}{N = {{{floor}\left\lbrack \frac{32}{N_{\;{DOPS}}(c)} \right\rbrack} + {{floor}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{{N_{\;{DOPS}}(a)} + {N_{\;{DOPS}}(b)} + {N_{\;{DOPS}}(c)}} \right\rbrack}}} & (11)\end{matrix}$

Equations for calculating frame lengths in the respective channels canbe derived as represented by the following Equations (12) to (14) usingthe Equation (11), where the frame lengths in the channels are LENGTH(A), LENGTH (B), and LENGTH (C), respectively, and the frames areallocated in descending order of transmission rate (starting from theChannel-A). The Equations (12) represent a case where final data of theMPDU ends in the Channel-A, the Equations (13) represent a case wherethe final data of the MPDU ends in the Channel-B, and the Equations (14)represent a case where the final data of the MPDU ends in the Channel-C.

$\begin{matrix}{\begin{matrix}{{{LENGTH}(A)} = {{\left( {N - 1} \right) \times {N_{DOPS}(a)}} - 3 +}} \\{{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack}\end{matrix}{{{LENGTH}(B)} = {{\left( {N - 1} \right) \times {N_{DOPS}(b)}} - 3}}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - 3}}\left( {{Where},{{{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} \leq {N_{DOPS}(a)}}} \right)} & (12) \\{{{{LENGTH}(A)} = {{\times {N_{DOPS}(a)}} - 3}}{{{LENGTH}(B)} = {{\left( {N - 1} \right) \times {N_{DOPS}(b)}} - 3 + {{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack}}}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - 3}}\left( {{Where},{{N_{DOPS}(a)} < {{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{{N_{DOPS}(a)} + {N_{DOPS}(b)} + {N_{DOPS}(c)}} \right\rbrack} \leq {{N_{DOPS}(a)} + {N_{DOPS}(b)}}}} \right)} & (13) \\{{{{LENGTH}(A)} = {{N \times {N_{DOPS}(a)}} - 3}}{{{LENGTH}(B)} = {{N \times {N_{DOPS}(b)}} - 3}}\begin{matrix}{{{LENGTH}(C)} = {{\left( {N - 1} \right) \times {N_{DOPS}(c)}} - 3 +}} \\{{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack}\end{matrix}\left( {{Where},{{{N_{DOPS}(a)} + {N_{DOPS}(b)}} < {{{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack}\mspace{14mu}{or}}},{{{mod}\left\lbrack \frac{\left( {L - L_{HEADER}} \right) + 3}{\;{{N_{\;{DOPS}}\;(a)}\; + \;{N_{\;{DOPS}}\;(b)}\; + \;{N_{\;{DOPS}}\;(c)}}} \right\rbrack} = 0}} \right)} & (14)\end{matrix}$

For reception, the Rx units 35-1, 35-2, and 35-3 perform the receptionof primitives, the reading of data, and the like from the physicallayers 31-1, 31-2, and 31-3 respectively and feed the results to theRxControl unit 36. The RxControl unit 36 integrally performs thecombining of frames received through the plurality of channels, the FCScheck, the writing of data to the buffer, the address decoding, thechannel status processing, and the like. In this embodiment, the MACaddress is included in the head of the frame received through eachchannel. No processing is, therefore, performed on a frame from anunexpected terminal. If it is necessary to transmit the ACK frame, areturning process through the protocol control unit 38 is performedsimilarly to the first embodiment.

FIG. 9 is an illustration of a data frame format according to the IEEE802.11a standard. FIG. 10 is an illustration of a method for dividing apart of a frame, differently from that shown in FIG. 8. In FIG. 10, MACheaders 41-1, 41-2, and 41-3, LLC headers/SNAP headers 42-1, 42-2, and42-3, and FCSs 44-1, 44-2, and 44-3, all of which are specified by anIEEE 802.11 standard, are added to divided frame bodies 43-1, 3-2, and43-3, respectively.

As described above, according to this embodiment, the radio signalconforming to the IEEE 802.11a standard, the IEEE 802.11b standard, theIEEE 802.11g standard, or the like is allotted to the plurality ofcommunication channels to be transmitted to the home/office wirelessnetwork. Here, the MAC sets the part of the frame as the divisiontarget, adds the rest of the frame to the divided frame divisions, andallots the added frame divisions to the physical layers. It is therebypossible to efficiently utilize the radio band, and thus greatly improvethe throughput, as compared with the conventional techniques.Furthermore, since the existing physical layers conforming to the IEEE802.11a, IEEE 802.11b, and IEEE 802.11g standards can be used, backwardcompatibility with respect to the existing systems can be maintained.The operations according to this embodiment are also applicable to aMIMO systems spatially having a plurality of channels.

Third Embodiment

An operation of the radio communication system according to a thirdembodiment will be specifically explained with reference to thedrawings. In this embodiment, only processes different from thoseaccording to the first and second embodiments will be explained.

FIG. 11 is an illustration of an example of dividing a frame to aplurality of channels. Each rectangle denotes an OFDM symbol, and Padbits and Tail bits added in the PHYs are shown. In the example of FIG.11, however, the number of OFDM symbols in a CH1 differs from those in aCH2 and a CH3. As shown in the first and second embodiments, therefore,it is necessary to add the Pad bits to make the numbers of OFDM symbolsequal.

According to this embodiment, therefore, the numbers of OFDM symbols aremade equal as shown in FIG. 12. FIG. 12 is an illustration of oneexample of this embodiment, in which a frame is divided to a pluralityof channels. Each rectangle denotes an OFDM symbol. Pad bits and Tailbits added in the PHYs are shown. Furthermore, in FIG. 12, a MAC Padindicating that the Pad bits have been added in the PHY by the MAC isadded, whereby the numbers of OFDM symbols are equal similarly to thefirst and second embodiments. It is noted that each frame is allotted inunits of OFDM symbol in the order of CH1 to CH3.

FIG. 13 is an illustration of a service field in the frame conforming tothe IEEE 802.11 standard. In this embodiment, a MAC_PAD_USAGE fieldindicating whether the MACPad is ON or OFF, a division number field, afield for a total number of divisions, and a COPY field indicatingwhether the same frames are copied in the channels are allocated toService [7:15] currently secured as Reserved. These fields can bearranged in any order.

FIG. 14 is an illustration of a communications status between radiostations that perform communications using a plurality of channels. At aradio station 60, first, when it is determined that the numbers of OFDMsymbols are not equal among the channels as shown in FIG. 11 when theframe is divided, the MAC Pad is added so that the data extend over thenext OFDM symbol as shown in, for example, FIG. 12. It is thenregistered in the MAC_PAD_USAGE field in the Service field of thetransmission frame that the MAC Pad has been added. Furthermore, at theradio station 60, necessary information is written in the divisionnumber field indicating the order in which the frames are allocated tothe channels, and into the field for the total number of divisionsindicating how many channels are used in communications, respectively.If the same frame is transmitted to each channel, then ON or OFFinformation is written into the COPY field, and the generated frames arethen transmitted to a radio station 61.

In this embodiment, the MAC_PAD_USAGE field, the division number field,the field for the total number of divisions, and the COPY field areallocated to the Reserved field in the Service field. However, thepresent invention is not limited thereto, and frames may be expanded inthe MAC or PHY per channel.

At the radio station 61 of the reception side, if the frames arereceived from the radio station 60 of the transmission side, theMAC_PAD_USAGE field, the division number field, the field for the totalnumber of divisions, and the COPY field are checked.

If the frame is copied in the COPY field, the following operation isperformed using frames which have been normally received through thechannels. If it is indicated by the COPY field that the frame has beendivided and transmitted, the frame divisions are combined based on thedivision number field and the field for the total number of divisions.In the combining process, information on the Pad bits added in the MACor PHY is detected based on the MAC_PAD_USAGE field notified in eachchannel, to delete unnecessary Pad bits. If the number of receivedchannels is smaller than a value written in the field for the totalnumber of divisions, this indicates that the frames have not beenreceived successfully, and an error processing is performed,accordingly.

As described above, according to this embodiment, the transmission sideadds the MAC_PAD_USAGE field, the division number field, the field forthe total number of divisions, and the COPY field. It is therebypossible to accurately detect how the Pad is inserted in each channel.In addition, since the information indicating the order in which theframe is allotted to each channel is inserted, at the reception side, itis possible to know the steps for combining the frames. The operationsaccording to this embodiment are applicable to the base stations and theradio terminals described in the previous embodiments.

INDUSTRIAL APPLICABILITY

As explained above, the base station and the radio terminal according tothe present invention are useful for the communication system thattransmits and receives the radio signal according to an IEEE 802.11wireless LAN standard and particularly suited to the communicationsystem for broadening the band using the plurality of communicationchannels.

1. A base station for a wireless network system realizing band-wideningusing a plurality of communication channels, the base stationcomprising: a plurality of physical layers corresponding to theplurality of communication channels, and each that transmits andreceives a radio signal conforming to a predetermined standard using acorresponding communication channel; and a media access control(hereinafter, “MAC”) layer, wherein the MAC layer includes, atransmitter control that divides an entire data frame conforming to thepredetermined standard from a head of the data frame, in accordance witha transmission rate of each physical layer, and allots the divided dataframe to the physical layers so that burst times of the communicationschannels are substantially equal, a protocol control that dynamicallycontrols the number of random access slots according to a slot use rate,and a receiver control that combines data frames received via aplurality of communication channels through operations opposite to thoseperformed when transmitting.
 2. The base station according to claim 1,further comprising: a determining unit that determines the transmissionrate of each communication channel, a frame allotment ratio between thecommunication channels, and a transmission data amount in eachcommunication channel, for the MAC layer to carry out the allotment andthe combination corresponding to the plurality of communicationchannels.
 3. The base station according to claim 1, further comprising:a protocol control unit conforming to the predetermined standard andusing a carrier sense multiple access/collision avoidance (CSMA/CA)protocol.
 4. The base station according to claim 1, wherein fortransmission, a frame having a frame length shorter than that of thedata frame is not divided and the same frame having a same rate istransmitted to each communication channel, and for reception, if oneframe having a frame length shorter than that of the data frame isreceived normally, the received one frame is recognized as a frametransmitted from a transmission side.
 5. The base station according toclaim 1, wherein if a number of communication channels used is one, thedivision and the combination are not carried out, and the physical layercorresponding to the used communication terminal transmits and receivesthe radio signal conforming to the predetermined standard.
 6. The basestation according to claim 1, wherein equal frames are allowed to betransmitted simultaneously using the plurality of communicationchannels.
 7. The base station according to claim 1, further comprising:a protocol control unit conforming to the predetermined standard andusing a polling control.
 8. The base station according to claim 1,wherein the plurality of communication channels are selectable accordingto a frequency, a space, or a combination of the frequency and thespace.
 9. The base station according to claim 1, wherein if theplurality of communication channels are used, a division number, a totalnumber of divisions, a Pad insertion method, and information indicatingwhether a same frame is copied for the plurality of communicationchannels are included in the data frame.
 10. A base station for awireless network system realizing band-widening using a plurality ofcommunication channels, the base station comprising: a plurality ofphysical layers corresponding to the plurality of communicationchannels, and each that transmits and receives a radio signal conformingto a predetermined standard using a corresponding communication channel;and a media access control (hereinafter, “MAC”) layer, whentransmitting, that divides a part of a data frame conforming to thestandard from a head of the part of the data frame, in accordance with atransmission rate of each physical layer, and allots the divided part ofthe data frame to the physical layers so that burst times of thecommunications channels are substantially equal, and when receiving,that combines data frames received via a plurality of communicationchannels through operations opposite to those performed whentransmitting.
 11. The base station according to claim 10, furthercomprising: a determining unit that determines the transmission rate ofeach communication channel, a frame allotment ratio between thecommunication channels, and a transmission data amount in eachcommunication channel, for the MAC layer to carry out the allotment andthe combination corresponding to the plurality of communicationchannels.
 12. The base station according to claim 10, furthercomprising: a protocol control unit conforming to the predeterminedstandard and using a carrier sense multiple access/collision avoidance(CSMA/CA) protocol.
 13. The base station according to claim 10, whereinfor transmission, a frame having a frame length shorter than that of thedata frame is not divided and the same frame having a same rate istransmitted to each communication channel, and for reception, if oneframe having a frame length shorter than that of the data frame isreceived normally, the received one frame is recognized as a frametransmitted from a transmission side.
 14. The base station according toclaim 10, wherein if a number of communication channels used is one, thedivision and the combination are not carried out, and the physical layercorresponding to the used communication terminal transmits and receivesthe radio signal conforming to the predetermined standard.
 15. The basestation according to claim 10, wherein equal frames are allowed to betransmitted simultaneously using the plurality of communicationchannels.
 16. The base station according to claim 10, furthercomprising: a protocol control unit conforming to the predeterminedstandard and using a polling control.
 17. The base station according toclaim 10, wherein the plurality of communication channels are selectableaccording to a frequency, a space, or a combination of the frequency andthe space.
 18. The base station according to claim 10, wherein if theplurality of communication channels are used, a division number, a totalnumber of divisions, a Pad insertion method, and information indicatingwhether a same frame is copied for the plurality of communicationchannels are included in the data frame.
 19. A radio terminal for awireless network system realizing band-widening using a plurality ofcommunication channels, the radio terminal comprising: a plurality ofphysical layers corresponding to the plurality of communicationchannels, and each that transmits and receives a radio signal conformingto a predetermined standard using a corresponding communication channel;and a media access control (hereinafter, “MAC”) layer, wherein the MAClayer includes, a transmitter control that divides an entire data frameconforming to the standard from a head of the data frame, in accordancewith a transmission rate of each physical layer, and allots the divideddata frame to the physical layers so that burst times of thecommunications channels are substantially equal, a protocol control thatdynamically controls the number of random access slots according to aslot use rate, and a receiver control that combines data frames receivedvia a plurality of communication channels through operations opposite tothose performed when transmitting.
 20. The radio terminal according toclaim 19, further comprising: a determining unit that determines thetransmission rate of each communication channel, a frame allotment ratiobetween the communication channels, and a transmission data amount ineach communication channel, for the MAC layer to carry out the allotmentand the combination corresponding to the plurality of communicationchannels.
 21. The radio terminal according to claim 19, furthercomprising: a protocol control unit conforming to the predeterminedstandard and using a carrier sense multiple access/collision avoidance(CSMA/CA) protocol.
 22. The radio terminal according to claim 19,wherein for transmission, a frame having a frame length shorter thanthat of the data frame is not divided and the same frame having a samerate is transmitted to each communication channel, and for reception, ifone frame having a frame length shorter than that of the data frame isreceived normally, the received one frame is recognized as a frametransmitted from a transmission side.
 23. The radio terminal accordingto claim 19, wherein if a number of communication channels used is one,the division and the combination are not carried out, and the physicallayer corresponding to the used communication terminal transmits andreceives the radio signal conforming to the predetermined standard. 24.The radio terminal according to claim 19, wherein equal frames areallowed to be transmitted simultaneously using the plurality ofcommunication channels.
 25. The radio terminal according to claim 19,further comprising: a protocol control unit conforming to thepredetermined standard and using a polling control.
 26. The radioterminal according to claim 19, wherein the plurality of communicationchannels are selectable according to a frequency, a space, or acombination of the frequency and the space.
 27. The radio terminalaccording to claim 19, wherein if the plurality of communicationchannels are used, a division number, a total number of divisions, a Padinsertion method, and information indicating whether a same frame iscopied for the plurality of communication channels are included in thedata frame.
 28. A radio terminal for a wireless network system realizingband-widening using a plurality of communication channels, the radioterminal comprising: a plurality of physical layers corresponding to theplurality of communication channels, and each that transmits andreceives a radio signal conforming to a predetermined standard using acorresponding communication channel; and a media access control(hereinafter, “MAC”) layer, when transmitting, that divides a part of adata frame conforming to the predetermined standard from a head of thepart of the data frame, in accordance with a transmission rate of eachphysical layer, and allots the divided part of the data frame to thephysical layers so that burst times of the communications channels aresubstantially equal, and when receiving, that combines data framesreceived via a plurality of communication channels through operationsopposite to those performed when transmitting.
 29. The radio terminalaccording to claim 28, further comprising: a determining unit thatdetermines the transmission rate of each communication channel, a frameallotment ratio between the communication channels, and a transmissiondata amount in each communication channel, for the MAC layer to carryout the allotment and the combination corresponding to the plurality ofcommunication channels.
 30. The radio terminal according to claim 28,further comprising: a protocol control unit conforming to thepredetermined standard and using a carrier sense multipleaccess/collision avoidance (CSMA/CA) protocol.
 31. The radio terminalaccording to claim 28, wherein for transmission, a frame having a framelength shorter than that of the data frame is not divided and the sameframe having a same rate is transmitted to each communication channel,and for reception, if one frame having a frame length shorter than thatof the data frame is received normally, the received one frame isrecognized as a frame transmitted from a transmission side.
 32. Theradio terminal according to claim 28, wherein if a number ofcommunication channels used is one, the division and the combination arenot carried out, and the physical layer corresponding to the usedcommunication terminal transmits and receives the radio signalconforming to the predetermined standard.
 33. The radio terminalaccording to claim 28, wherein equal frames are allowed to betransmitted simultaneously using the plurality of communicationchannels.
 34. The radio terminal according to claim 28, furthercomprising: a protocol control unit conforming to the predeterminedstandard and using a polling control.
 35. The radio terminal accordingto claim 28, wherein the plurality of communication channels areselectable according to a frequency, a space, or a combination of thefrequency and the space.
 36. The radio terminal according to claim 28,wherein if the plurality of communication channels are used, a divisionnumber, a total number of divisions, a Pad insertion method, andinformation indicating whether a same frame is copied for the pluralityof communication channels are included in the data frame.
 37. A methodof transmission used in a transmission device included in a wirelesscommunication system transmitting a data frame by using a plurality ofcommunication channels with different transmission rates, the methodcomprising: a frame allotment step of dividing one data frame intoframes of differing length corresponding to each of the plurality of thecommunication channels having said different transmission rates so thattransmission burst times are substantially equal for the plurality ofcommunication channels.
 38. A method of transmission used in atransmission device included in a wireless communication systemtransmitting a data frame by using a plurality of antennas, the methodcomprising: a transmission rate determination step of determining atransmission rate for each of the plurality of antennas; and a frameallotment step of dividing one data frame into frames of differinglength corresponding to each of the plurality of antennas havingdifferent transmission rates so that transmission burst times aresubstantially equal for the plurality of antennas.
 39. A method oftransmission used in a transmission device included in a wirelesscommunication system transmitting a data frame by using a plurality ofcommunication channels, the data frame being classified into a firstframe or a second frame shorter than the first frame, the methodcomprising: a transmission rate determination step of determining atransmission rate for each of the plurality of communication channels;and a frame allotment step of allotting the date frame divided into thefirst frame or the second frame to the plurality of communicationchannels, wherein if the transmitted data frame is the first frame, thetransmission rate determination step includes setting a plurality oftransmission rates to the plurality of communication channels, and theframe allotment step includes dividing one data frame into frames ofdiffering length corresponding to each of the plurality of communicationchannels having different transmission rates so that transmission bursttimes are substantially equal for the plurality of communicationchannels with set transmission rates, and if the transmitted data frameis the second frame, the transmission rate determination step includessetting a common transmission rate to the plurality of communicationchannels, and the frame allotment step includes allotting the data frameeach of the plurality of communication channels.
 40. A method oftransmission used in a transmission device included in a wirelesscommunication system transmitting a data frame and a control frame, themethod comprising: a transmission rate determination step of determininga transmission rate for each of the plurality of communication channels;and a frame allotment step of allotting the data frame or the controlframe to the plurality of communication channels, wherein if the dataframe is transmitted, the transmission rate determination step includessetting plurality of transmission rates to the plurality ofcommunication channels, and the frame allotment step includes dividingone data frame corresponding to each of the plurality of communicationchannels so that transmission burst times are substantially equal forthe plurality of communication channels with set transmission rates, andif the control frame is transmitted, the transmission rate determinationstep includes setting a common transmission rate to the plurality ofcommunication channels, and the frame allotment step includes allottingthe transmitted control frame to each of the plurality of communicationchannels.
 41. The method according to claim 40, wherein the controlframe includes a Clear To Send Signal.
 42. A transmission deviceincluded in a wireless communication system transmitting a data frame byusing a plurality of communication channels with different transmissionrates, comprising: a frame allotment unit that divides one data frameinto frames of differing length corresponding to each of the pluralityof communication channels having said different transmission rates sothat transmission burst times are substantially equal for the pluralityof communication channels.
 43. A transmission device includes in awireless communication system transmitting a data frame by using aplurality of antennas, comprising: a transmission rate determinationunit that determines a transmission rate for each of the plurality ofantennas; and a frame allotment unit that divides one data frame intoframes of differing length corresponding to each of the plurality ofantennas having different transmission rates so that transmission bursttimes are substantially equal for the plurality of antennas.
 44. Atransmission device included in wireless communication systemtransmitting a data frame by using a plurality of communicationchannels, the data frame being classified into a first frame or a secondframe shorter than the first frame, comprising: a transmission ratedetermination unit that determines a transmission rate for each of theplurality of communication channels; and a frame allotment unit thatallots the data frame divided into the first frame or the second frameto the plurality of communication channels, wherein if the transmittedframe is the first frame, the transmission rate determination unit setsa plurality of transmission rates to the plurality of communicationchannels, and the frame allotment unit divides the data frame intoframes of differing length corresponding to each of the plurality ofcommunication channels having different transmission rates so thattransmission burst times are substantially equal for the plurality ofcommunication channels with set transmission rates, and if thetransmitted data frame is the second frame, the transmission ratedetermination unit sets a common transmission rate to the plurality ofcommunication channels, and the frame allotment unit allots the dataframe to each of the plurality of communication channels.
 45. Atransmission device included in a wireless communication systemtransmitting a data frame and a control frame, comprising: atransmission rate determination unit that determines a transmission ratefor each of the plurality of communication channels; and a frameallotment unit that allots the data frame or the control frame to theplurality of communication channels, wherein if the data frame istransmitted, the transmission rate determination unit sets a pluralityof transmission rates to the plurality of communication channels, andthe frame allotment unit divides one data frame corresponding to each ofthe plurality of communication channels so that transmission burst timesare substantially equal for the plurality of communication channels withset transmission rates, and if the control frame is transmitted, thetransmission rate determination unit sets a common transmission rate tothe plurality of communication channels, and the frame allotment unitallots the transmitted control frame to each of the plurality ofcommunication channels.
 46. The method according to claim 45, whereinthe control frame includes a Clear To Send Signal.